It is known in the art to generate EUV light from the production of a plasma of an EUV source material which plasma may be created by a laser beam irradiating the target material at a plasma initiation site (i.e., Laser Produced Plasma, “LPP”) or may be created by a discharge between electrodes forming a plasma, e.g., at a plasma focus or plasma pinch site (i.e., Discharge Produced Plasma “DPP”) and with a target material delivered to such a site at the time of the discharge. Target delivery in the form of droplets of plasma source material, which may, e.g., be mass limited for better plasma generation conversion efficiency and lower debris formation, are known techniques for placing the plasma source material at the appropriate location and at the appropriate time for the formation of the plasma either by LPP or DPP. A number of problems are known to exist in the art regarding the delivery timing and positioning of the target at the plasma initiation site which are addressed in the present application.
Commercially available lithium has purity of 99.99% (100 ppm). A method of lithium purification is distillation as discussed in U.S. Pat. Nos. 4,738,716 and 4,842,254 at a temperature of, e.g., 550° C. for several hours (6 hours). This can decrease the concentrations from 200 ppm to 5 ppm for Na and from 100 ppm to 2 ppm for K. Both Na and K are condensed on a surface with temperature of 100° C.